The Internet retailer also issued a sales forecast for the current period that was ahead of Wall Street's expectations, and announced a surprise $2 billion share buyback — even though the stock has been trading near its record high.

The news pushed the Seattle company's stock up $2.94, or 2.3 percent, to $128.97 in after-hours trading Thursday. Before the financial results were announced, Amazon shares had closed the regular session up $3.28, or 2.7 percent, at $126.03.

For the period ended Dec. 31, Amazon reported profit of $384 million, or 85 cents a share, compared with profit of $225 million, or 52 cents a share, for the same period the previous year. Sales rose 42 percent to $9.52 billion.

Analysts expected earnings of 72 cents a share on revenue of $9.04 billion, according to consensus forecasts from Thomson Reuters.

"These were very strong results, even better than the high expectations going into the report," said Colin Sebastian of Lazard Capital Markets, who added that the company "continues to take significant market share in e-commerce."

Tim Boyd of MKM Partners called the quarter a "huge beat" for Amazon, noting the company also guided its revenue forecast above current estimates.

Overall sales of media products grew 29 percent to $4.7 billion for the quarter compared with a year earlier.

Sales of electronics and other general merchandise jumped 60 percent to $4.6 billion.

Sales in the company's "other" category, which includes its nascent Web-services business, grew 32 percent to $231 million.

Dan Geiman, an analyst with McAdams Wright Ragen in Seattle, said the quarter was "extremely strong" and the results suggest Amazon took some share of the online retail market from competitors.

"It's just huge growth, given that consumers are still under quite a bit of pressure," he said. "The economy still isn't that great."

For the first quarter, Amazon predicted revenue in the range of $6.45 billion to $7 billion. Analysts were looking for $6.36 billion.

Speaking to analysts during a conference call, Chief Operating Officer Tom Szkutak said there are still plenty of product categories and geographic markets Amazon could enter.

As in the past, Amazon did not say how many Kindles it has sold so far, though CEO Jeff Bezos said in a statement that "millions" of people now own the electronic-book reader.

He also said Amazon is selling six Kindle books for every 10 physical copies for the titles available in both formats.

Amazon previously said it had reached a Kindle milestone Christmas Day, when it sold more copies of e-books than physical copies for the first time.

The company, however, is encountering more competition from a growing number of e-reader competitors — including Apple, which announced its tablet-style multimedia player, the iPad, on Wednesday.

The new $2 billion share buyback Amazon announced replaces a previous buyback of $1 billion approved in 2008.

"I found the buyback surprising, with the shares at this level," said Lazard's Sebastian.

Amazon stock hit a 52-week closing high of $142.25 on Dec. 2.

Boyd, at MKM Partners, said the move shows Amazon is "committed to returning cash to shareholders and, do not view their stock as overvalued by any means."